Fault And Status Reporting Between Output Modules And Controllers - Allen-Bradley 1756-IA8D User Manual
Controllogix digital i/o modules
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Fault and Status Reporting
between Output Modules
and Controllers
Module Fault Word
Fuse Blown Tag
ControlLogix fast digital output modules multicast fault and status data to any
owner-controller or listening controller. Like input modules, output modules
maintain a Module Fault word, the highest level of fault reporting. However,
output modules use an additional word to indicate a fault condition.
Table 24
lists the fault word and the associated tag you can examine in program
logic to indicate when a fault has occurred for a fast output module.
Table 24 - Fault Words on Fast Output Modules
Word
Module Fault
All words are 32-bit, although only the number of bits appropriate for each
module's density are used. For example, the 1756-OB16IEF module has a
Module Fault word of 32 bits. But, because the module is a 16-point module,
only the first 16 bits (0...15) are used in the Module Fault word.
Bits set in the FuseBlown tag are logically entered into the Module Fault word.
Depending on the module type, a bit set in the Module Fault word can mean
multiple things, as indicated in the table.
Table 25 - Bits Set in Module Fault Word
Condition
Communication fault
Fuse blown
The following illustration provides an overview of the fault reporting process for
digital output modules.
Bit 31
A communications fault sets all bits in the Module Fault word. A Fuse Blown
condition sets the appropriate bit in the Module Fault word.
A blown fuse for any point sets the bit for that point in the FuseBlown tag and
also sets the appropriate bits in the Module Fault word. In the example above,
the bit for the FuseBlown tag is set indicating a blown fuse at point 9.
Bits set for the Fault input tag indicate I/O data may be incorrect due to a fault
due to one of these conditions:
• FuseBlown = 1
• PWMCycleTime outside the valid range of 0.001...3600.0 seconds
• PWMOnTime outside the valid range of 0.0002...3600.0 seconds
or 0...100 percent
• PWMCycleTime ≤ PWMOnTime
Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Input Tag Name
Description
I:Fault
Provides fault summary reporting. Available on all digital output
modules.
Bit set
All 32 bits are set to 1, regardless of the module's density.
Only the bit affected is set to 1.
Fast Module Features
Bit 0
1
1
Chapter 5
107
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